Advances in semi-conductor processing and logic design have permitted an increase in the amount of logic that may be present on integrated circuit devices. As a result, the power demands of integrated circuits, such as microprocessors, have drastically increased. As a remedy, many processors now support multiple power/operating states. And the transitions between performance states often cause large variations on the voltage supply when the current demand of processors similarly fluctuates. As an example, in a very short period processor current demand may transition from 1× to 50× due to these operating/performance state transitions. Here, the voltage supply is severely degraded—large overshoot or undershoot from nominal voltage—as a consequence of the current demand transitions.
Typically there have been two approaches to handling this voltage supply degradation. In one post-design scenario, a large amount of decoupling capacitors are added to a processor package and/or motherboard to reduce voltage droops. Yet, adding capacitors is both monetarily expensive and physically expensive (the capacitors take up additional critical signal routing/placement space). In a second, pre-design scenario, processor designers take into account the voltage supply issues by adding a guard-band (a tolerance band that the processor still operates appropriately). However, an increase in guard-band both results in an additional power losses and performance degradation, since the designers are constrained by designing to worst case scenarios.
For example, FIG. 2 illustrates an embodiment of a change in current demand. At 205, an increase in current demand of a processor occurs. As a result, the voltage supply, in reaction to the increase in current demand, undershoots (or droops) at 210. Here, the operating voltage of a processor is decreased. And the performance of the processor is similarly decreased. In addition, at 215, the current demand is decreased, which results in overshoot 220. The change in magnitude between undershoot 210 to overshoot 220 is often referred to as guard band 225. And as described above, as guard-band 225 increases the use of capacitors or worst case design increases, which potentially results in more cost, less routing space, degraded performance, and greater power consumption.